Method of extracting lead from lead sulphide ores and concentrates



Feb. 25, 1947. BM. s. KALLING E'r Al.A 2,416,628 K METHOD OF EXTRACTING LEAD FROM LEAD SULPHIDE ORES AND CONCENTRATES Filed Dec. 4, 1945 (z5/40 ox/oE FAD co/vcn/mqrf (ogg (PAN/AMY ,eaasrfo /w/o (Pass/.snl ALso SLAG ma co/vcmrmrf) ma sum/mrs) PRoouc/NG .50mm/mss), (ORE) ausm/f TAN/vae Patented Feb. 25, 1947 METHOD vor Inx'rxrlc'rnsiol LEAD .ImoM

LEAD SULPHIDE oREs AND coNoEN-,-

TRATES Bo Michael Sture VKallin'gg,y Djursholm, Sven Johan VValldn, Stockholm, and 'G-ustarf' Tanner,`

Sundsvall, Sweden,

i ass'gncrs4 l Gruvaktiebolag, Stockholm Sweden, a .stock .company limited v.of Sweden to 'Boldens jointe .Appiicati'on 'December 4, 19.43, Serial No. 512,977 'In Sweden March 11,' 1941 'Known 'methods for extracting lead concentrates of high lead content and ne grain can .not be employed without some special preparatory treatments which involve certain metallurgical inconveniences as well as considerable cost. A charge for sintering and smelting in a blast furnace should not contain more than 45 to 55 per cent of lead whereas flotation concentrates can be had with a content of more than 80 per cent of lead. If the concentrate has a high content of lead it must be dilutedby mixing it with some relatively diliicultly fusible material prior to the sintering operation. Melting in a blast furnace also requires such a low content of sulphur vin the charge that the sulphur has to be removed in two stages, such as by a 'double sintering of the Whole diluted mixture or of part thereof, or by roasting and sintering the same. The simple open hearth process which can be employed for a' coarse material having a high content of lead and a low content Aci gangue can not be used for otation concentrates owing to their too low permeability to gases.

It has been proposed to eiect smelting of the lead sulphide ore and oxidizing its content of sulphide to metal in a single operation kbut such proposals have not led to any practical results ow-y ing to the reason, among others, that such `an operation will result in high losses of lead with the flue gases. This is easily explained from the fact that the vapor pressure of the lead sulphide is 109 millimeters at its melting point, viz. 1114" C., 319 millimeters at l200'C. and-937 millimeters at l500 C. l

This invention relates to a method forlextracting lead from lead sulphide ores or concentrates which consists in smelting the material and oxidizing it under conditions that will cause only such part of the lead sulphide to be oxidized as is required for carrying out the process. The invention is characterized by smelting the material so as to form a solution containing lead sulphide and metallic lead together with sulphides of such impuritiesas may be formed, .and then oxidizing the lead sulphide contained 'in the solution and forming metallic lead. Metallic lead and lead sulphide are intel-soluble at the temperatures in question and the solution possesses a relatively low vapor pressure. Such a solution can be produced and oxidized without the lead sulphide being volatilized to an undesired extent.

The quantity of lead required for producing said solution may either be 'added to the molten lead sulphide in the form of metal or it may be produced in connection with the smelting of the 2 sulphide. `In`the lat-ter'case the lead dueedbyadding lead oxide, lead sulphate Aor lead oxide and carbon 'to the charge according to' anyl ci the known'zreact'ions as Vgiven by the following formulas: l

' Pbs+2Pbo=ePb+so2 Pbs+Pbso4=f2Pb+2so2 Y 1 bo+o=rt,L'Co' j s it has been found that the'smemng and oxi-` dizing operation can .be so conducted that the' necessary* amount of lead oxide and lead sulphate maybe obtained by recovering and `returning the iiue dust 'formed during thelead extracting operations.

The requisite oxidation products may also b'e added in 'such a way that part ofthe lead sulphide is roasted before being added 'to the smelted lead sulphide. It is to be recommended in this case only to roast the material partially which may be performed at such a low temperature that .no sin-tering will .take place, vfor example in the usual shelved furnace. .If lead oxide ore is to be .had it may of course be directly smelted 'together with the sulphide cre,

.In other words, and with .reference .to the addsmelting of the lead sulphide material is performed in an' electric furnace vwhere the quantity o-f 'gas which escapes from the mass of material and 'which carries with 'it Volatilizedlead sulphide is lrelatively small compared to the quantityfof gases'l'passing through a furnace heated by combustion gases such as an open hearth furnace.A v Y The subsequent oxidizing process may be perl formed in a converter of a known type where air is blown through the bath containing the mixture of lead and lead sulphide. In employing the usual bessemer process too great losses of lead will be caused by gasification, even at a relatively low content of sulphide. It has also proved dilcult to obtain a refractory lining for the furnace which will be resistant to the lead oxide formed during the blowing operation by may be proin lead dueto the low solubilityof lead y,sulphide in the slag. A,During .the oxidizing Voperation the quantity of slag must be Ykept as low as possible as the lead oxide will very easily form a slag.

Much better results are obtained if the oxida" tion of the Vbath is performed'4 in such a way that airis blown along the surfaceof the bath or obliquely downwards towards its surface. In thisA way thecontent of lead sulphide at the surface of the bath will be steadily diminishing so that the voiatilizanon of the sulphide Win be less man yl i ifV the content thereof was distributed evenly throughout the melt, as is often the case when' 'the bessemer process is employed. A thorough mixing in the bath will be obtainedin spite of i f er in lead, will be heavier than the underlying er in sulphur. In this caseit will be much'rcasier to make the lining resistant to anyv attack from Y such rlead oxide as may be formed, because the bath will keep relatively still in the furnace.

As an example of the result which may be obtained by the process according to the present invention, and in order to show how the operation may be performed, the following dataare given: `In an 'electric smelting furnace a bath of slag was heated by passing an electric current vthrough it. vDuring a'period of eight hours a charge of the following composition was fed on to the bath:

, 1020 kilograms of a otation concentrate com- The charge was fed to the surface of the bath in batches at every 15th second and the previous batch had melted before a new batch was added. The solution of lead in lead sulphide showed the of glass added. This second batch of slag was removed after stillanother blowing period of 11/2 hours.Y After the blowing had been continued for5 hours in all, there then remained in the furnace a bath of metallic lead covered by a thin layer consisting of a stone rich in copper and a slag of glass. 422 kilograms of raw lead could be tapped from the furnace and also 138V -kilograms of slag and 242 kilograms of stone and refuse were also obtained. About 40 per cent of .the content of lead had been Volatilized and thereafterrecovered in aYV gas purifying plant, whereas thev remaining lead not accounted for .had been retained inthe furnace or been-re' f moved .with rthe slag from the furnace.

'erably, better results may be obtained with still vricher lead concentrates.

the diminished motion of the bath dueto thel circumstance that the uppermost layer, being rich- The accompanying drawing illustrates schematically a ow sheet of the process according to the present invention.

Having thus described our invention,lwe de- `vclare that what we claim is:

l. `A method for extracting lead from a material selected from the class consisting of lead sulphide ores and concentrates of such ores, com. prising melting said material in admixture with an added substance comprising at least one oxyfollowing percentages of ingredients at the middle yof the tapping:

`YS Ib Fe Zn Cu gen-containing` compound of lead selected from the class consisting of rlead oxide and lead sulphate so as to form a leadsulphide-metallic lead'solution having, under the conditions obtaining in the melt, a relatively lowrvapor pressure as compared to that of lead sulphide alone, and then oxidizing the lead sulphide in the solution thus obtained to form metallic lead.

2. A method as claimed in claim 1, characterized in that said material is melted under conditions such that a minimum of gaseous products is present -in the melting zone by melting said material in an electric furnace, thereby reducing the loss of lead by Volatilization.

3. A method as claimed in claim 1, characterized in that the oxidation operation is effected by blowing air against the surface of the bath.

4. A method as claimed in claim l, characterized in that the lead content of the melt is regulated by admixing a carbonaceous reducing material with the charge.

BO MICHAEL STURE KALLING.

SVEN JOHAN WALLDEN.

GUSTAF TANNER.

l REFERENCES CITED The following references are of record ln the Vfile of this patent:

UNITED STATES PATENTS OTHER REFERENCES Y Hofman, Metallurgy of Lead, published in 1918, by the McGraw-Hill Book Co. of New York.

Pages 72 and 87.

Consid- 

